A sagittal saw is a powered surgical tool that is typically used in an orthopedic surgical procedure. A sagittal saw generally includes a handpiece that houses a motor and the complementary control circuit that regulates actuation of the motor. Extending forward, distally, from the handpiece is a head. Internal to the head is an oscillating shaft. Removably attached to the oscillating shaft is a saw blade. The exposed distal front edge of the blade is formed with teeth. The teeth cut the tissue against which the blade is applied. A drive mechanism internal to the housing generates power. This power is applied to actuate the oscillating shaft so that the shaft and the attached blade move in a back-and-forth pattern in which the blade is aligned. When the saw is so actuated, the blade teeth move in a back-and-forth pattern against the tissue against which they are applied. Due to the forward pressure applied by the surgeon holding the saw, the teeth cut and separate the hard tissue against which the blade is applied.
A sagittal saw is often used in an orthopedic surgical procedure to selectively remove bone. One particular type of orthopedic surgical procedure in which the saw is used is a joint replacement procedure. As implied by the name, in this type of procedure, the surgeon resects the bone between the joints in the patient and substitutes an artificial joint.
In an orthopedic surgical procedure it is important to ensure that, when the section to be resected is separated from the remaining bone, the section is removed along precise lines. Accuracy is mandatory because the substitute joint typically has a component designed to precisely fit in the space left by the cut line of the bone left in place.
To ensure the cuts are properly formed in the bone, the surgeon typically first mounts a cutting guide, sometimes called a jig, to the bone adjacent the location at which the cut is to be made. One type of cutting guide is in the form of a block with a precisely shaped set of slots. The slots define the lines along which the bone is to be cut. The surgeon removes the bone by sequentially inserting the saw blade in the slots. Once the blade is inserted in a slot, the saw is actuated. This arrangement enables the surgeon to cut the bone along the precisely defined lines.
Presently available sagittal saws and their complementary blades adequately cut the bone against which the blades are applied. However, some limitations are associated with these assemblies. Many commercially available sagittal saws are provided with planar blades that oscillate. The blade inevitably rubs against the cutting guide material that defines the slot(s) in which the blade is inserted. This repetitive contact wears away the slot-defining material. Eventually the slot may become so wide that it no longer precisely defines the intended cut line. Once a cutting guide is so worn, it needs to be replaced.
It should similarly be appreciated that, the repeated abutment of the saw blade against the cutting guide can cause the guide to move. If an accurate cut is desired this movement is, at a minimum, undesirable.
Moreover, the wearing of the material forming the cutting guide generates a fine dust of material. Some of this dust inevitably settles on the surgical site at which the procedure is being performed. Consequently, during the procedure, the surgical personnel are required to spend an appreciable amount of time flushing the site to remove this dust. Having to repeatedly perform this process runs counter to one of the primary goals when performing surgery; that one should perform the procedure as quickly as possible to minimize the time that both the exposed tissue is open to infection and the patient is held under anesthesia.
As discussed above, the oscillating blade of a current surgical saw will repeatedly gall the surfaces of the cutting guide forming the slot in which the blade is inserted. One further disadvantage of this blade galling it consumes power. Many sagittal saws are battery powered. The power expended overcoming the blade galling-induced friction reduces the overall amount of power available to actuate the saw. This reduces the overall amount of time the battery, on a single charge, is able to power the saw.
Moreover, as a consequence of the saw blade galling against a surface of the cutting guide, then pulling away from this surface, there is some jerking of the blade. The jerking motion is transferred from the blade through the handpiece into the hand of the surgeon holding the saw. Consequently, the surgeon must exert some muscle control to hold the handpiece steady when he/she is exposed to this jerking motion.
Also, an inevitable result of the back-and-forth motion of the blade, the sagittal saw invariable vibrates. Again, the surgeon is required to engage in some conscious or unconscious physical effort to hold the saw steady when it vibrates. Over time, having to so hold the saw to overcome this vibration can be significantly mentally and physically fatiguing.
The Applicant's Assignee's U.S. patent application Ser. No. 10/887,642, filed 9 Jul. 2004, U.S. Patent Publication No. 2006/0009796 A1, now U.S. Pat. No. 7,497,860, incorporated herein by reference, discloses a saw and complementary saw blade that are designed to overcome, if not essentially eliminate, the limitations described above. The blade assembly of this invention includes a bar to which a blade head is pivotally mounted. Drive rods disposed in the bar extend proximally rearward. The blade bar is removably attached to a head that is part of that is part of the saw of this invention. The drive rods are coupled to an oscillating shaft integral with the saw head. When the saw of this invention is actuated, the oscillating shaft moves back and forth. This movement, in turn, causes the drive rods to reciprocate. The drive rods thus oscillate the blade head around the pivot point against which it is mounted.
The above saw and blade assembly are designed so that, only the distally located blade head oscillates. The blade assembly bar remains static. This eliminates many of the problems that otherwise occur if the whole of the blade assembly is allowed to move back and forth.
The assembly of the above application works well. However, this assembly relies on removable threaded fasteners to removably hold the blade assembly to the saw head. Surgical personnel must use a tool to first remove, and, then, replace the saw blade. Having to perform these steps in surgery can lengthen the overall time it takes to perform the procedure. Moreover, this action requires the surgical personnel to account for the threaded fasteners as well as the component to which they are attached.
Also, debris from cut tissue can enter the bars of some blade assemblies. These debris can potentially inhibit blade head oscillation.
Furthermore, it is desirable to provide a sagittal saw with an assembly that allows the saw head to be rotated, indexed, around the longitudinal axis of the head. This is because often it is desirable to position the head so that the complementary blade assembly is disposed in a plane that is not simply perpendicular to the axis that extends top-to-bottom through the saw. Therefore, this type of saw normally includes an indexing assembly that allows the saw head to be rotated, indexed, to a select angular orientation and locked in place.
A conventional indexing mechanism typically includes a single biasing member, a spring, that holds the head in a fixed index orientation. Often, surgical personnel find it difficult to manually overcome the force imposed by this spring in order to rotate the saw head.